Ribulose, 1,5-bisphosphate (RuBP) carboxylase catalyzes the primary assimilation of carbon dioxide. Based on prior active-site and effector-site modification and regulation studies, we intend to: (a) probe the differential regulation of the two activities catalyzed by RuBP carboxylase/oxygenase. (b) Determine the stoichiometry of substrate (RuBP) and effector binding in the Co(III)-enzyme complex of spinach and Rhodospirillum rubrum carboxylase/oxygenase. (c) Isolate, purify, and sequence peptide(s) containing active-site residues from the R. rubrum enzyme. (d) Probe further into the mechanism of the oxygenase reaction catalyzed by RuBP carboxylase/oxygenase.